FIG. 13 partially illustrates a plan-view structure of a conventional thermal print head (see, e.g., JP2976087B). A thermal print head X shown in FIG. 13 includes a substrate 91, heating portions 92 made of resistor layer provided on the substrate 91, an electrode layer 93 for applying an electric current to the heating portions 92 and a drive IC 94. The heating portions 92 are finely divided in a primary scanning direction x and are independently heated by the drive IC 94. The electrode layer 93 includes a common electrode 95 and a plurality of individual electrodes 96 arranged along the primary scanning direction x. As shown in FIG. 13, electrode wiring lines 95a of comb teeth shape extend from the common electrode 95 at a regular interval. One end section of each of the individual electrodes 96 is positioned between the mutually adjoining electrode wiring lines 95a. Pad portions 97 are provided in the other end sections of the respective individual electrodes 96. The pad portions 97 are connected to pads 94a of the drive IC 94 through wires. The drive IC 94 can heat the heating portions 92 positioned in desired positions by selectively applying the electric current to the individual electrodes 96.
In order to arrange the heating portions 92 of, e.g., 200 dpi, namely 8 dots in a length of 1 mm, the respective individual electrodes 96 have a fine pitch of 0.125 mm. As a result, the electrode wiring lines 95a and the individual electrodes 96 are formed into fine wiring patterns. A pad surface having a specified width is needed to properly perform wire bonding. In the example illustrated in FIG. 13, the width of the respective pad portions 97 is secured by arranging the pad portions 97 in a staggered pattern. If the pad portions 97 are arranged in line, the sections of the wires making contact with the pad portions 97 tend to becomes dense, which may possibly make it difficult to bond the wires.
In a process of manufacturing the thermal print head X, an open-short test is conducted between the individual electrodes 96 or pulse trimming is performed to make the resistance value of the heating portions 92 equal to an expected value. When performing these tasks, for example, a test probe 98 is bought into contact with each of the pad portions 97 as shown in FIG. 14.
As can be seen in FIG. 14, a probe mark 97a is generated on the pad surface if the test probe 98 is bought into contact with each of the pad portions 97. The portion having such a scratch is not suitable for use in wire bonding. For this reason, it is necessary that each of the pad portions 97 be divided beforehand into a probe contact pad 97b and a bonding pad 97c for wire bonding. JP2976087B illustrates an example in which the probe contact pad 97b is formed in a position spaced apart from the bonding pad 97c. In any case, the dimension of each of the pad portions 97 in a secondary scanning direction y tends to become greater.
In this aspect, the plurality of pad portions 97 may be arranged at an increased density in the primary scanning direction x. As the density of the plurality of the pad portions 97 increases, the dimension in the secondary scanning direction y of a pad installation region 97A needed to install the pad portions 97 tends to increase. This has an adverse affect in reducing the size of the thermal print head X.